Power MOSFETs are a type of Metal Oxide Semiconductor Field Effect Transistor (MOSFET) that is designed to handle significant power levels. Some of these devices are designed to switch high currents and to have low on resistance. Some of these devices are designed to tolerate high voltages across the device's terminals. The voltage tolerance and current requirements have resulted in device configurations different from traditional MOSFET designs. One such device configuration involves trenches, which have been used to provide vertical channel conduction for such power MOSFETS.
Some of these high-voltage power MOSFETS are manufactured using trenches that have dielectric sidewalls and a dielectric bottom isolating a field plate within the trench from surrounding semiconductor material. The field plate can be biased to deplete majority carriers from the surrounding semiconductor material. Some trench MOSFETS are manufactured between closely spaced field plates that reside in closely spaced trenches. In such cases, the semiconductor material between these closely spaced trenches can be substantially depleted of majority carriers throughout. When the semiconductor material is so depleted of majority carriers, a high-voltage drain bias can be distributed across the depletion regime so that the drain/body interface is not exposed to an excessive voltage—a voltage that can cause avalanche breakdown.